The present invention relates generally to electroslag refining, and, more specifically, to control thereof.
Electroslag refining (ESR) may be used for melting and refining iron, nickel, or titanium based alloys. The unrefined alloy is provided in the form of an ingot electrode which is suspended inside a water-cooled copper crucible. A suitable slag is disposed at the bottom of the crucible and is electrically resistively heated and melted, with the molten or liquid slag then being used to melt the lower tip of the electrode immersed therein. A power supply is electrically joined to the crucible and the electrode, and electrical current flows through the electrode, molten slag, and crucible for resistively heating the slag which melts the ingot tip as it is lowered into the crucible during operation.
Droplets of the molten electrode fall by gravity through the molten slag and undergo refining in which oxide inclusions in the metal are removed by and dissolved in the molten slag. The refined metal is denser than the slag and accumulates at the bottom of the crucible, with the slag floating thereatop.
The bottom of the crucible includes a cold-walled induction-heated guide tube (CIG) having a central orifice drain through which a liquid stream of the refined metal may be drained by gravity from the crucible. This refined stream is an ideal liquid metal source for many solidification processes including powder atomization, spray deposition, investment casting, melt-spinning, strip casting, and slab casting.
Since the melt temperature of the discharge stream is substantial, variations in the drain rate affect the solidification of the stream as it is deposited in the subsequent solidification processes such as spray deposition. Relatively slow draining increases solidification speed, and fast draining decreases solidification speed, with both extremes adversely affecting material properties of the solidified metal.
The flowrate, or pour rate, of the draining stream should match the melt rate and is affected by the diameter of the drain, the pressure heads of the molten metal and liquid slag thereatop, and the differential pressure above the slag and below the drain. The drain diameter is affected by the thickness of the skull of solidified molten metal in the drain, which in turn is affected by the amount of induction heating energy supplied into the drain.
The pressure heads of the molten metal and slag are affected by their respective heights, with the molten metal height being variable, with the slag height typically being a constant. And, the differential pressure inside and outside the crucible is controlled by the respective gas pressures thereat.
U.S. Pat. No. 5,809,057-Benz et al discloses an exemplary apparatus for electroslag refining, and subsequent spray atomization, over which the present invention is an improvement. Since the drain rate is affected by many operating parameters, it will vary unless those parameters are controlled.
Accordingly, it is desired to measure the drain rate of the crucible for controlling the electroslag refining process, for in turn controlling and optimizing the metallurgical properties of the resulting solidified metal.